I've seen in many publications, that GTP (green flurorescent Protein) targeted molecules in mice are detected with a camera, without opening the mouse in any surgery. How is this possible? Is it possible that flurorecence penetrates Skin?

for those who dont't know: GTP is a Protein from a jelly fish. When it is illuminated with light of short wavelength it reflects light of longer wavelength and become visible. This protein is attached by molecular cloning to an other protein, so the targeted protein can be detected by fluorescence.

The abbreviation is GFP.

When the GFP gene is expressed in skin cells (keratinocytes) then it will fluoresce under the appropriate wavelength and be visible because it is at the skin surface. If however the gene is targeted to deeper tissues eg heart or brain then as you say that tissue needs to be directly exposed in order for the fluorescence to be visualised.